1. Field of the Invention
The present invention relates to a dielectric loaded antenna apparatus for use in a microwave band, a quasi-millimeter wave band, or a millimeter wave band, an array antenna apparatus including the dielectric loaded antenna apparatus, and a radio communication apparatus including one of the dielectric loaded antenna apparatus and the array antenna apparatus. In particular, the present invention relates to a dielectric loaded antenna apparatus with a loaded dielectric having an inclined radiation surface, an array antenna apparatus including the dielectric loaded antenna apparatus, and a radio communication apparatus including one of the dielectric loaded antenna apparatus and the array antenna apparatus.
2. Description of the Related Art
Conventionally, a dielectric loaded antenna apparatus having a loaded dielectric which is loaded on a feeder circuit which is constituted by a microstrip line, a waveguide or the like has been often used as an antenna for use in a radio communication apparatus in a microwave band, a quasi-millimeter wave band or a millimeter wave band, as disclosed in, for example, the Japanese patent laid-open publication No. 2002-185240, and a prior art document of Tetsuo Tsugawa et. al, “Fat Dielectric Loaded Antenna”, Proceedings of 1999 IEICE (The Institute of Electronics, Information and Communications Engineers in Japan) General Convention, B-1-119, pp. 119, issued by IEICE, March 1999.
FIG. 41 is an exploded perspective view showing a configuration of a conventional waveguide feeding type dielectric loaded antenna apparatus. The conventional waveguide feeding type dielectric loaded antenna apparatus shown in FIG. 41 is characterized in that a feeding waveguide 4 and a radiation waveguide 7 are each formed by a lower conductor substrate 11 and an upper conductor substrate 12, and in that a loaded dielectric 108 including a circular dielectric column is provided on the upper conductor substrate to cover a radiation opening 107 of the radiation waveguide 7. A lower rectangular groove 2 having a rectangular cross section is formed on a top surface of the lower conductor substrate 11. One end of the lower rectangular groove 2 passes through a bottom surface of the lower conductor substrate 11 to be connected with a feeding opening 1, and another end of the lower rectangular groove 2 is connected with a lower radiation waveguide chamber 5 having a rectangular cross section. The lower radiation waveguide chamber 5 is formed by boring the lower conductor substrate 11 in the thickness direction thereof from the top surface by a predetermined depth. An upper rectangular groove 3 which has a rectangular cross section and which corresponds to the lower rectangular groove 2 is formed on a bottom surface of the upper conductor substrate 12. One end of the upper rectangular groove 3 is connected with an upper radiation waveguide chamber 6 which passes through the upper conductor substrate 12 in the thickness direction and which has a rectangular cross section.
Further, when the lower conductor substrate 11 and the upper conductor substrate 12 are superimposed on each other so that the lower rectangular groove 2 opposes to the upper rectangular groove 3 and so that the lower radiation waveguide chamber 5 opposes to the upper radiation waveguide chamber 6, the lower rectangular groove 2 and the upper rectangular groove 3 constitute the feeding waveguide 4 having a rectangular cross section and also the lower radiation waveguide chamber 5 and the upper radiation waveguide chamber 6 constitute the radiation waveguide 7 having a rectangular cross section. A length of the radiation waveguide 7 in a guide or tube axial direction or a guide or tube direction (namely, the vertical direction) is set to n×λg/2 (where n is a natural number) when a guide wavelength that corresponds to an operating wavelength of the antenna apparatus is set to λg. The loaded dielectric 108 is fixedly attached onto the radiation opening 107 of the upper conductor substrate 12 so that a central axis in the vertical direction of the radiation waveguide 7 coincides with the central axis in the vertical direction of the loaded dielectric 108.
An electromagnetic wave input from the feeding opening 1 progresses or travels into the feeding waveguide 4, and the progressive electromagnetic wave passes through the radiation waveguide 7, then being fed to the loaded dielectric 108. In this case, there appear two types of waves, i.e., the electromagnetic wave that passes through the loaded dielectric 108 and a surface wave that progresses or travels along a surface of the loaded dielectric 108. By determining dimensions of the loaded dielectric 108 so that the two type waves are made to be in phase on a horizontal surface S0 that is a top surface or a radiation surface of the loaded dielectric 108, the present dielectric loaded antenna apparatus operates as a high-gain antenna. The dielectric loaded antenna apparatus can attain high gain characteristics with a small size, so that the loaded antenna apparatus can operate as a high efficient antenna.
Now, an xyz coordinate system as shown in FIG. 41 with a center of the radiation opening 107 of the radiation waveguide 7 set as an origin will be referred to hereinafter. In the configuration shown in FIG. 41, it is assumed, for example, that the lower conductor substrate 11 is made of aluminum and has horizontal dimensions of 100 mm×100 mm and a thickness of 3 mm and that the upper conductor substrate 12 is made of aluminum and has horizontal dimensions of 100 mm×100 mm and a thickness of 2.5 mm. It is also assumed, for example, that the cross section of the feeding waveguide 4 when the lower conductor substrate 11 is coupled with the upper conductor substrate 12 has a vertical length of 3.76 mm and a horizontal length of 1.88 mm, the horizontal cross section of the radiation waveguide 7 has cross sectional dimensions of 2.8 mm×2.8 mm, the column-shaped loaded dielectric 108 is made of polypropylene having a dielectric constant of 2.26, and has dimensions of 6 mm in a diameter φ and 7 mm in a length L.
FIG. 42 is a graph showing a radiation directivity pattern on the xz plane of the dielectric loaded antenna apparatus of FIG. 41 which was manufactured to have the above-mentioned dimensions. As shown in FIG. 42, the radiation directivity pattern of the conventional dielectric loaded antenna apparatus has a beam direction of a +z direction that is a front direction perpendicular to the top surface of the upper conductor substrate 12. In other words, if the column-shaped or cubic-shaped loaded dielectric 108 is employed, the radiation directivity pattern has a beam direction in a direction toward a direction in which the dielectric is loaded on the conductor substrate. This is because on the surface of the loaded dielectric 108, the amplitude and the phase of the propagating electromagnetic wave are axial symmetric with respect to the central axis of the loaded dielectric 108. Therefore, in order to radiate the electromagnetic wave in a desirable direction other than the +z direction, it is necessary to direct the whole dielectric loaded antenna apparatus to the desirable direction.
Furthermore, since the dielectric loaded antenna apparatus has a high gain characteristic, the dielectric loaded antenna apparatus has such a feature of a narrower beam of the radiation directivity characteristic thereof, then having a narrower coverage area. In a frequency band such as a millimeter wave band whose spatial loss is relatively large, the antenna apparatus is required to have a high gain upon designing telecommunication circuits. However, depending on the purpose, the antenna apparatus is required to have a wider coverage area, and then the antenna apparatus is required to satisfy the above two contradicting relations simultaneously.